LAS VEGAS  It was the morning after San Diego State’s signature moment of the season, a 55-34 victory at Viejas Arena against a New Mexico team that hadn’t scored so few points in 36 years and would win the Mountain West by three games.

Xavier Thames was at his apartment, and his parents, in town for the game, came to visit him. They knocked on the door. There was a lapse before he answered it.

He didn’t need to say anything, didn’t need to wince, didn’t need to grab his lower back in pain. Mothers just know these things, and Angie Thames knew her baby was hurting.

“It took me a while to get to the door and open it,” Thames said, “and my mom was like, ‘Xavier, you all right?’ I said, ‘No, my back is killing me, Mom.’ I couldn’t bend over. I could barely walk. It was bad.”

He admits it. The thought seeped into his consciousness: Man, I don’t think this is going to get any better. I might be done for the season.

Thames can punctuate the sentence with a smile now, standing inside the Thomas & Mack Center on the eve of the semifinals of the Mountain West tournament and a rematch with No. 15 New Mexico (6 p.m., CBS Sports Network). He still gets sore after games. He still hasn’t recovered the fitness from not practicing for two months. But he can bend over fine, and he’s not hobbling across the room to answer the door anymore.

On the stat sheet: He has scored 18 points in back-to-back games and double figures in three straight for the first time since December, before he reached for a pass in a Jan. 2 game against Cal State Bakersfield and felt a twinge in his lower back. In Wednesday’s 73-67 win against Boise State in the Mountain West tournament quarterfinals, he also had season highs in rebounds (six) and assists (five).

At the press conference:

Boise State coach: “One of the things that maybe gets lost on San Diego State is they didn’t have X for a lot of their games in January. That kid’s really important to this team. If you add him to this team, they’re a team that probably contends for the league title.”

New Mexico coach Steve Alford: “I think he’s the key … They’ve had some ups and downs during the year because of Thames not being healthy, and he seems to be very healthy now.”

Thames had five points on 1-of-7 shooting and one assist in 23 minutes in the Jan. 26 game against New Mexico. After he woke up the next morning with “the worst pain I’ve felt in a long time – a long, long time,” Thames met with Fisher, trainer Tom Abdenour and doctors, and they agreed three weeks of not practicing but trying to play games wasn’t working.

They shut him down completely for two weeks.

The Aztecs lost their next game, 70-67 at Air Force, along with any realistic hope of contending for a conference title. It was a calculated decision, though, knowing that a healthy X in March was more valuable than a hobbled X in February.

Tapley bailed out the Aztecs in the next game, draining a 3-pointer with 2.8 seconds left to beat Boise State at home. Thames has played in all nine games since, gradually increasing his minutes, gradually increasing his fitness, gradually increasing his confidence.

He seemed to turn a corner last Saturday at Boise State, with 16 points in 18 second-half minutes. On Wednesday in Las Vegas, he played a team-high 37 minutes and didn’t sub out in the second half.

“He makes a difference for us,” Fisher said, “there’s no question about that.”

It means a lock-down defender (he helped frustrate Boise State’s Derrick Marks into a 0-of-12 start). It means another perimeter scorer. It means making that extra dribble drawing a help defender and giving a shooter that extra split-second to set his feet. It means the return of SDSU’s screen-and-roll game.

Next up: The winner advances to the Mountain West tournament final on Saturday at 3 p.m. against UNLV or Colorado State.

Aztecs outlook: This is a rematch of the 2012 championship game (New Mexico won 68-59) and the third time in the last four years they have met in the MW tournament. The Aztecs are 11-2 over the last five years at the conference tournament, and a win would put them in their fifth straight final. Wednesday’s 73-67 victory against Boise State bumped SDSU’s RPI up to No. 28. A win or loss today won’t have any bearing on whether they make the NCAA Tournament, but it could impact their seed. Most prognosticators have them on the 8-9 line, with the prospect of facing a No. 1 seed in the second round. A win over a New Mexico team with a No. 2 RPI, you’d think, could elevate them to a 7. Having a healthy Xavier Thames should help. In two games playing with an injured back this season, he shot a combined 4 of 20 against the Lobos; in SDSU’s win at New Mexico last year, he had 22 points on 7-of-11 shooting.

Lobos outlook: As their bigs go, so go the Lobos. In the first meeting with SDSU, a 55-34 loss (and their fewest points in the shot-clock era), Kirk and Cameron Bairstow scored a combined two points on 1-of-12 shooting. In the second meeting, a 70-60 win, they had 41. SDSU employed a similar defensive game plan both times, faking the post double-team while staying home on the perimeter shooters. Said Coach Steve Alford: “I thought our spacing was really bad in Game 1 and we turned the ball over so much (17 times) that we let them get out on transition. In Game 2, our spacing was better, we didn’t turn the ball over (nine times), we went inside out, we got ball reversals and we were able to create a little bit more freedom to our offense.” So what do the Aztecs do this time? Play the post straight up? Bring the double team? Fake the double team again? It makes for an intriguing strategic decision.